1. Field of the Invention
The present invention relates generally to surveying a radio audience to determine the audience rating indicative of the extent to which the audience is tuned at any given time to a particular radio station and, more particularly to an apparatus for monitoring the status of use of a car radio receiver mounted on an automobile for family or business use.
2. Description of the Related Art
In recent years, radio audience survey, which has been conducted on the basis of radio sets installed at sample households, is required to also cover car radios mounted on various types of automobiles. This is because the number of people listening to radio programs over car radios has rapidly increased as a result of ever-expanding motorization.
A conventional apparatus for identifying a radio station to which a car radio is tuned employs, as disclosed in the Japanese Patent Application Kokai Publication No. 7-327017, a monitoring unit having a reference radio receiver capable of being tuned to any radio stations to which the car radio is tunable. The loudspeaker output of the car radio is picked up by a microphone and supplied to the monitoring unit, where the microphone output, i.e., a reception audio signal, is compared with a reference audio signal supplied from the reference radio receiver. If the comparison result shows the coincidence between the two, the radio station is identified by the station name stored in advance in the monitoring unit. If not, the reference receiver is tuned to the next radio station, to which the car radio is possibly tuned. The procedure is repeated until the coincidence is achieved, thereby to identify the radio station to which the car radio is actually tuned. Data relating to the identified radio station and its associated time are sent periodically through a radio link to survey center.
While such a conventional apparatus can generate data on a certain sample car radio tuned to a particular radio station at a particular time, it cannot provide data on individuals, who were actually in the driver's seat listening to the programs of interest. More specifically, the conventional apparatus based on the vehicle-by-vehicle data collection is not adapted to provide data on individual members of a family, for example, who have equal access to the automobile carrying the sample car radio. This presents some problems because the audience rating survey often requires certain criteria such as age, income, sex and level of education, in order to generate more specific data for determining advertising rates and for adjusting programming.
Similarly, the conventional apparatus is not capable of measuring the length of idle time, in which the car radio could have been tuned to any one of the radio stations but was actually kept in OFF state. Data relating to such idle time, which reflects the potential demand for new programs, can be very important for broadcasters' program planning.
Furthermore, since the conventional monitoring apparatus relies for its power supply on the vehicle-mounted storage battery used also for engine starter, continued power-ON state of the monitoring apparatus can cause the discharge of the battery beyond the allowable limit, making it impossible to start the engine of the vehicle. Also, the lowered output voltage of the storage battery can cause the monitoring apparatus to cease the transmission of collected data to the survey center. Under such situation, the survey center cannot take any effective countermeasure, due to the lack of timely information from the monitoring apparatus.
Moreover, the use of microphone to provide the reception audio signal in the conventional monitoring apparatus tends to adversely affect the reliability of the radio station identifying function, because various background sounds and noises, the difference in antenna gain between the car radio and the reference receiver, unbalanced stereophonic audio outputs from loudspeakers, the unavoidable instantaneous reception interruption, and the like can make the proper comparison of the reception audio signal with the reference receiver output impossible.